1. Field of the Invention
The present invention relates to a recording method, recording apparatus, transmitting apparatus, reproducing method, reproducing apparatus, receiving apparatus, recording medium, and transmission medium in which a p-bit input data word is converted to a q-bit (q>p) code word using a plurality of coding tables, and when a code word string produced by directly coupling the code words is recorded in a recording medium such as an optical disk and magnetic disk and reproduced, or is transmitted via a transmitting portion, a coding rate is raised, a density for a recording medium or a transmission medium is raised, and at the same time, an ability of correction of a burst error can be enhanced.
2. Description of the Related Art
Generally, a pit length to be recorded in an optical disk has a restriction on a minimum run length (minimum pit or land length) due to optical transmission characteristic for recording and reproducing and physical restraint about pit generation and further, a restriction on a maximum run length (maximum pit or land length) for a reason of facilitation of clock generation. Further for protection of a servo band, and the like, it is necessary to modulate signals to be recorded so that the signals have a suppression characteristic of low-pass components of the signals.
As a conventional modulation method satisfying these restrictions, in which the minimum run length (hereinafter referred to also as a minimum reverse interval) is 3T (T=a period of channel bit), and a maximum run length (hereinafter referred to also as a maximum reverse interval) 11T, an 8 to 14 modulation (EFM) method for use in a compact disk (CD), and EFM+ method for use in a digital versatile disk (DVD) have been well known.
First, in EFM modulation for use in the compact disk (CD), inputted 8-bit (1 byte) digital data is converted to 14-bit run length limited code (hereinafter referred to as a code word) satisfying the run length restriction such that the minimum run length is 3T and the maximum run length is 11T. Furthermore, a 3-bit connection bit for controlling a digital sum value (DSV) and holding a run length restriction rule is attached between the converted code words so that an EFM modulated signal is generated.
In this case, for the minimum run length of 3T, a minimum number of “0” included between logical values “1” and “1” in code words is d=2. On the other hand, for the maximum run length of 11T, a maximum number of “0” included between the logical values “1” and “1” in the code words is k=10. Moreover, the 3-bit connection bit disposed for controlling the DSV and holding the run length restriction rule in order to reduce a DC component and low-pass component of the modulated signal is connected between the 14-bit code words. Thereby, the EFM modulated signal satisfies a run length restriction rule RLL (d, k)=RLL (2, 10) that the minimum run length is 3T and the maximum run length is 11T.
Next, in the EFM+ method used for the digital versatile disk (DVD), the inputted 8-bit digital data is converted to a 16-bit code word, these code words are directly coupled to one another without using any connection bit, and thereby 8 to 16 modulation is executed so as to satisfy the run length restriction rule RLL (2, 10) that the minimum run length is 3T and the maximum run length is 11T. As compared with CD, a DVD has a shorter minimum mark length that is shorter than half of that of a CD and has a higher track density with the track pitch of 0.74 μm that is higher than double of that of CD. A user recording capacity of a single-sided, single-layer disk is 4.7 GB.
Furthermore, as a replacement of a disk in the current generation in which a red laser beam is used, manufacturers are now studying a next-generation super high-density optical disk that uses a violet laser beam (GaN), and the recording capacity of the next-generation optical disk is said to exceed 20 GB. Here, a modulation system by a high coding rate has been studied in order to perform high-density recording with respect to the optical disk. Accordingly, the minimum mark length and track pitch are naturally reduced, and values are said to be reduced to about ½ of those of DVD. Under such circumstances, a defect of the optical disk developed by a defect of a signal surface generated during disk manufacturing or by dust or a scratch during use of the optical disk, if any, would be twice as large as that on the DVD in view of a relative data length, and an error is generated in reproduced data.
On the other hand, in general, in the optical disk, a parity bit is added in order to subject the data to be recorded to an error correction processing. A unit of the error correction is called an ECC block. For example, the ECC block in a conventional recording medium such as DVD is shown in (A) and (B) in FIG. 1.
That is, as shown in (A) in FIG. 1, in the DVD, product coding (product coding is a coding of an error correction such as a product error correction coding) is performed for a set of 192 rows×172 columns data in order to generate 10 columns of PI parity (inner parity) for each row, and 16 rows of PO parity (outer parity) for each column. As a result, a 208×182 error correction code (ECC) block is constituted. Moreover, as shown in (B) in FIG. 1, during recording, one row of PO parity data is inserted every 12 rows of data to interleave data with PO parity data. Moreover, for the ECC block, first to 208-th rows are recorded on the optical disk in order.
In this method, up to 16 rows may be erasure-corrected with the PO parity data. This means that a data error caused by a continuous defect of up to 6 mm on the optical disk may be corrected. Such continuous error is generally called a burst error. When the track linear density is double in this format, the maximum length of the correctable defect will be reduced to 3 mm. Moreover, five symbols (bytes) may usually be corrected with PI parity data and, if there is no random error, the maximum length of a correctable burst error on the DVD is about 10 μm. Therefore, when the track linear density is doubled, the maximum length of the defect correctable with the PI parity data is about 5 μm.
Meanwhile, if there is a random error, the length of the burst error correctable with the PI and PO parity data becomes much shorter in the conventional method and on the recording medium described above. It should be noted that PO rows of the DVD are interleaved with data rows, not to distribute burst errors, but to keep a parity data ratio in a sector to be constant. Therefore, there is no effect of increasing the correction length.
To solve the problem, there is a method of increasing the number of parity data units and increasing the correction length. However, since redundancy of parity data increases with respect to the ECC block, this method is very disadvantageous for the high-density recording to the super high-density optical disk being studied.